Resilient piston pin bushing



June17,1947.r wawmsmw 2,422,327

RESILIENT PISTON PIN BUSHING Filed June 10, 1944 i IWTOR. I fffwwwm Patented June 17, 1947 RESILIENT PISTON PIN BUSHING William B. Winslow, chicago, 111., assigner to `Allen Trask, Chicago, Ill.

Application June 10, 1944, Serial No. 539,656

6 Claims.

This invention relates to piston pin bushings, and more particularly to piston pin bushings of a resilient material for use in refrigeration compressor pistons.

In many refrigeration installations it is highly desirable to have the compressor function as quietly as possible. Household refrigerators are one example of such installation. Another example is the self-contained unit air conditioner.

When the compressor in units of this class is of the reciprocating type using a piston in a cylinder for effecting compression, a clicking noise is often caused by the sudden pressure drop in the cylinder as the piston starts on the suction.

stroke from upper dead center. It has been learned from careful laboratory experiments that this particular clicking noise referred to does not result from a sudden contact of mechanical parts. Compressors have been built wherein the piston pin was fit to the piston with a ,light press t that would admit of no relative movement in the direction of piston travel, and wherein the connecting rod fit on the piston pin and crankshaft would not permit a relative movement between said parts, and yet a clicking noise would occur at the point of sudden pressure reduction in the cylinder at the start of the suction stroke.

It was found that this clicking noise is louder in fast operating compressors than in those being driven at a relatively slow speed. It is particularly noticeable in compressors being driven betweenV 1700 R. P. M. and 1800 R. P. M. by standard 60 cycle alternating current motors having four poles in the stator.

It has also been discovered that a compressor operating at a ve pound gauge suction pressureV that noise gradually diminish in intensity as the suction pressure is gradually increased. The clicking noise has been observed to diminish to inaudibility upon an increase of suction pressure to 40 pounds gauge pressure. During these experiments the head pressure, or end pressure of compression, was approximately 100 pounds per square inch gauge pressure. These observations bear out the conclusion that the said clicking noise is caused by the sudden reduction of pressure in the compressor cylinder at the beginning of the suction stroke, for when the amount of pressure reduction is diminished to a certain extent by an increase of suction pressure the clicking noise stops.

A similar clicking noise is often observed in steam radiators which are vcold when steam is 2 rst admitted. In this instance there is no question as to the possibility that the click be originated by sudden mechanical contacts, for there are no separate parts within the radiator. Likewise, in the radiator, the clicking noise is caused by a sudden reduction of pressure. The sudden condensation of steam causes the sudden pressure drop, and the resultant clicking noise.

It is highly desirable to eliminate the clicking noises of refrigeration compressors. Precision iitting parts are now the rule, yet in spite of this and all other mechanical refinements of compressors as known and constructed today, an objectionable clicking noise persists in many compressors. Y

I have discovered that by the use of piston pin bushings constructed of a resilient material the maximum frequency of pressure waves within the cylinder can be reduced below the frequency that produces an audible clicking noise.

An object of this invention is a resilient piston pin bushing that will limit the frequency of pres. sure waves with the cylinder of a compressor to less than a disagreeably audible frequency.

A further object is a resilient piston pin bushing which will retain a piston pin in substantially xed relation to a connecting rod.

Still another object of this invention is a pair of resilient piston pin bushings which will retainl a piston pin in substantially fixed relation to a piston.

Improved volumetric efliciency of compression is also an object of this invention.

These and other objects and advantages of the invention will more fully appear from the following description made in connection with the accompanying drawings, wherein like reference characters refer to the same parts throughout the Views, and, in which: v

Figure 1 is a perspective view of a resilient piston pin bushing adapted for use in an assembly including a connecting rod, a piston, and a piston D111;

Figure 2 is a vertical sectional view through a piston assembly which utilizes two bushings of the type shown in Figure 2; and

Figure 3 is a vertical sectional View through ak piston assembly utilizing the bushing in a different type of piston construction.

In Figure 1 the numeral 4 refers to the complete resilient piston pin bushing shown, This bushing is constructed preferably of a synthetic rubber such as Neoprene, having a durometer hardness reading of between 40 and 100 points. The selection of hardness is to be specifically determined by the mechanical requirements for the desired natural frequency of the piston on the resilient bushing. These mechanical requirements are met by the selection of appropriate relationship between the piston head area, the projected area and wall thickness of the bushing or bushings used, and the working pressures Within the cylinder generated by the piston. Annular anges 5 at each end of bushing d has a lcross section vthickness substantially equal toy that of the tubular body .of the bushing. It flares outwardly at an angle of approximately 4.5 degrees. Bushing Il has an in'.- ternal concentric annular rib 6 and anexternal concentric annular groove 'I in the plane of annular rib 6, of such proportions-that the Wall secisfmadeby first assembling the bushing 4 in contion of bushing 4 retains approximatelyan. equal thickness throughout its length.

In Figure 2, piston pin 8 has concentric annular grooves 9 near each end. Two bushings @arenassembled to piston pin 8 with their annular ribs 6 fitting in piston pin. grooves 9. This t estab,- lishes a substantially fixed relationship between. bushing 4. and piston pin .8. -Piston Ivfhasapiston pinhole .I-I yin. each side; each hole II having both its outer and .inner ends chamfered at an angle of 45 degrees as at .I 2 tomate withv external annular .flanges 5 of bushing il. The flanges .5 establish a substantially fixed .relationship .between bushingll and piston 1.0.

.Aconnecting rod L3 is assembled to piston I0 by means of they piston pin. 8. An oil hole I1! inthe connecting rod I3 is in registry with an annular oil groove I;5- midway between. the ends.

of' piston pin. 8. This structure described, and shown in Figure 2, is adapted for refrigeration compressors having pressure feed .of lubricating oilv through thev hole VIii. in connecting rod t3: to its bearing. on piston .pin 8.

'In Figure 3 .a piston pin IZB. has. an .annular groove I'I midway between its ends., This groove is of thesame shape and servesthe same .function as. the grooves 9 in piston pin .8. of Figure 2. The bushingV 4 is assembled to the. piston .pin I6 with its annular `rib 6 .fitting in the annular groove I'I. This fit substantially fixes the relationship between the bushing 4 and piston pin I6..

The connecting rod I8 has. a hole. to receive the bushing 4. Both endsof the saidconnecting rodhole .are chamfered at 45 degrees to .receive annular flanges 5. of bushing d, which .anges I maintain a substantially fixed relationship .between the bushings` and connecting rod I8.V This structure described', and shown in. Figure 3, is suitablefor compressors having splashrlubrication for the bearing ofthe piston pin |16 in the. piston I9.

The .assembly of the parts shownin. Figure. 2. is made'by rst assemblingone. ofthe bushings 4 to one end of piston pin B.. Next, a second bush.- ing I is assembled into the piston pinhole in one side of piston lil. The annular flange Sis flexed to a circumference equaling the' diameter ,of the. piston pin hole as it is inserted' and with a rotary motion it is pressed in. Next, the bearing of connecting rod I3" is aligned withthe piston pin holes II'ln thepiston I0; Next, the. end' ofthe piston pin 8 Without the bushing Aassembled,,is inserted in the-piston pinhole II inwhich there has not been a bushing assembled. The end of piston pin 8 passes through theV connecting roel4 bearing and-'enters thesecond 'bushing'iir as flanged olithe first' bushing assembled enters' thechamfenof' the piston pin hole in which the insertion hasbeen made. By flexing flange 5 'to the diameter ofthe piston pin hole Yand imparting a rotary mjotion'` as 4 it is pressed in, piston pin 8 and said rst essembled bushing 4 may be pressed into place in piston I8. When the leading end of the piston pin 8 reaches the internal annular rib 8 in the second bushing 4, the rotary motion and pressure used for assembling will cause annular rib 6 to flex into the annular groove 1 which is made of such size that this method of assembly may be executed. The continuation of rotarymotion and pressure will produce the-.alignment and assembly of parts as shown in Figure 2. The piston pin 8 will be retained in its operating position Within the piston I0, by the resistance of the internal ribs E and external flanges 5 to flexing.

VThe.assembly of the parts shown in Figure 3 necting rod I8. Next the connecting rod I8 is assem'hl'ed within the piston I8 so that its bearing is in alignment with the piston pin holes. Next, piston pin I6 is inserted in the piston pin hole on one side of the piston and. pressed through the bushing 4 in connecting rod i8 until it reaches its nal position wherethe internal annular rib.` 6 engages the annular groove I1 in the piston .pin

I6.. The pistonpin 1.6 will be retained in its oper-` ating position. within the piston I8, by theresistance-to ilexingof internal rib S and external ii'anges ,5; v

VIn operation the. heads of pistons I0 and I9' are subjected' to f-ull compressive forces .at. the end of the compression stroke and the bushings ..4 are'subjected to compression to the same degree. Immediately subsequent to the ending of the compression stroke the suction stroke begins, `and the fluid pressure withinthecylinder drops to the suction pressure ofv the fluid entering the compressor. The sudden release vo'f pressure from thepistons releases the compression pressure from bushings '4. which by .their elasticity then returnv to their normal balance of assembly stress within. the piston pin holes of the piston or the connect; ingY rod` as the case may be. Under the shock of sudden pressure reduction the pressure waves set up. Within'the cylinder cannot exceed the natural frequency of the pistons on. the resilient V'piston pin bushings. The resilience of the'bushi'ngs is.v such that `the piston Afrequency 'is lower than'the frequency of sound wavesv which are heard asa click' or' otherv objectionable sound. Thus the l resilient'hushings of this' invention eliminate 'an objectionablel sound' of compressor operation..

Sometirries refrigeration compressors are con'-A structed so that a greaterl than minimum volume of compressed iluid ispurposelyY retainedwithi'n presser is' rendered' more quiet by the increased`A volume of lie-expanding fluid.

However,A vre-emJanding fluidv in. a compressorv cyiinder'reduces the amount of l'ovv pressure Huidv that caribeA drawn in on the suction stroke. 'In

other words, the. volumetric efliciency `of 'the vc'on'rpressoris reduced. AWhen quietness of opera-4 tionis an important factor of compressor design...

thevoiumetriceiiiciency, andthus refrigeration ing the resulting Vhigh eilici'encyand refrigeration capacity. It eliminates the need for reduced refrigeration capacity for the purpose of obtaining quiet operation. Thus this invention attains its object of improved compressor eilciency.

Although I have illustrated and described a specific design of resilient piston pin bushing for refrigeration compressors, it is, of course, t be understood that various ychanges can be made in the form, details, materials and arrangement and proportions of the bushing and its associated parts without departing from the scope of my' invention.

What I claim is:

1. A cushioning device for use with a reciprocating piston adapted to operate in a cylinder, a connecting rod and a piston pin, wherein the piston is provided with a piston pin aperture having ilared ends, comprising a yieldable bushing adapted to t between said piston pin and said piston and in said opening, said bushing having outwardly ilared end portions adapted to fit the contour of said opening in said piston to prevent movement of said bushing relative to said piston.

2. A cushioning device for use with a reciprocating piston adapted to operate in a cylinder, connecting rod and piston pin, wherein said connecting rod is provided with a piston pin bearing aperture, comprising a yieldable bushing adapted to it within said connecting rod piston pin bearing aperture, said bushing having flared ends to prevent displacement oi the bushing relative to said connecting rod bearing aperture.

3. A cushioning device for use with a piston, a connecting rod and a piston pin, wherein said piston pin is provided with an annular groove, comprisinga sleeve-like bushing having an internal rib moulded to fit said annular groove and adapted when assembled into said annular groove to resist longitudina1 movement relative to said piston pin.

4. A cushioning device for use with a piston having a piston pin bore and a piston pin adapted to t within said bore, comprising a resilient bushing moulded to an external shape adapted for nesting into a portion of said piston bore and moulded to an internal shape adapted to be assembled contiguous with a portion of the eX- ternal surface of said piston pin, the said piston pin bore having an irregular shape longitudinally such that a exing of said resilient bushing is required for its assembly or disassembly within said piston pin bore, and the external shape of said piston pin being irregular longitudinally such as to require a ilexing of said resilient bushing for its assembly on or disassembly from said piston pin.

5. A cushioning device for use with a piston, a connecting rod and a piston pin wherein said connecting rod is provided with a bore adapted to receive said piston pin, comprising, a resilient bushing moulded to an external shape adapted for nesting into the bore in said connecting rod and moulded to an internal shape adapted to be assembled on a portion of the external surface of said piston pin lying within said bore in said connecting rod, said bore having an irregular shape longitudinally such that flexing of said resilient bushing is required for its assembly or disassembly within said yconnecting rod bore, and the ex. ternal shape of said piston pinbeing irregular longitudinally such as to require a exing of said resilient bushing for its assembly on or disassembly from said piston pin.

6. A cushioning device for use with a piston, a connecting rod and a piston pin, wherein said piston pin is provided with an annular groove, comprising a resilient sleeve-like bushing having an internal rib formed to t said annular groove and adapted, when assembled into said annular groove, to resist longitudinal movement relative to said piston pin.

WILLIAM B. WINSLOW.

REFERENCES CITED Thekfollowing references are of record in the le of this patent:

UNITED STATES PATENTS 

